Transcript Evidence Analyte/Characteristic Techniques Blood Ethanol

Lecture: Forensic Evidence
Physical Evidence
Any material either in gross or trace
quantities that can establish through
scientific examination and analysis
that a crime has been committed.
F o re n s ic la b o ra to rie s
Item s of p h ysica l e vid e n c e
id e n tifica tio n
e va lu a tio n
in d ivid u a liza tio n
Classification of Physical Evidence
• Trace evidence
extremely small items
• Direct evidence
stands on its own to prove an
alleged fact
• Prima facie evidence
evidence established by law
• Circumstantial
evidence
incriminates a person
• Exculpatory evidence
helps to prove that an
accused individual is not
guilty
Physical evidence utilization in other areas
of forensic investigation
• Provides investigative leads for a case
• Ties one crime to a similar crime or connects one
suspect with another
• Corroborates statements from witnesses to or
victims of a crime
• The elements of a crime help to determine what
will be useful as evidence.
• Besides knowing what types of evidence to search
for, it is necessary to know where evidence is most
likely to be found.
Characteristics of evidence
Class characteristics
features that place the item
into a specific category
Individual characteristics
features that distinguish one
item from another of the same
type
E x a m in a t io n a n d a n a ly s is o f p h y s ic a l
e v id e n c e
H ig h e s t d e g r e e o f s c ie n tific c e r ta in t y p o s s ib le w ith
c u r r e n t te c h n o lo g y
p h y s ic a l
id e n tific a tio n
c h e m ic a l
id e n tific a tio n
b io lo g ic a l
id e n tific a tio n
Evidence
Analyte/Characteristic Techniques
Blood
Ethanol
Drugs of abuse
Composition
Color
Fabric
Fibers
Glass
Shoes
Powder
Soil
Saliva stain
Hair
Composition
Physical properties
Refractive index
Magnesium
Miscellaneous
Drugs of abuse
pH
Iron
Proteins
DNA
Appearance
Headspace analysis GC GC/MS
FT-Raman spectroscopy
Visible, diffuse reflectance
spectroscopy
FT-IR microscopy
Solubility, melting point
Microscopy
Atomic absorption
spectrophotometry
Solid-phase extraction; LC
FT-IR
Potentiometry
UV-Visible Spectr.
Immunological tests
Short tandem repeat
DNA analysis
Microscopy
Evidence
Techniques
Gunshot residue
Atomic absorption spectrophotometry,
scanning electron microscopy
Visible reflectance, FT-IR microscopy, FTRaman
UV–vis, LC
FT-IR, UV–vis
Thermal analysis, FT-IR
Liquid- and solid-phase extraction, GC/MS
Fluorescent visualization
Atomic absorption spectrophotometry,
titrations
Clothing
Pen inks
Plastic fragments
Tire fragments
Food (poisoned)
Fingerprints
Metals
Arson samples
GC, GC/MS
X-Ray Diffraction
13-8 Crystal Structures
X-Ray Diffraction
One morning in the summer of 1961, hundreds of crazed birds attacked the seaside
town of Capitola, California. The birds "cried like babies" as they dove into streetlamps,
crashed through glass windows, and attacked people on the ground. Most of the birds
were sooty shearwaters, a normally nonaggressive species that feeds on small fish and
comes ashore only to breed. The incident fascinated Alfred Hitchcock, who frequently
vacationed in nearby Santa Cruz. He included newspaper clippings about the Capitola
attack in his studio proposal for The Birds, which appeared in cinemas two years later.
In the winter of 1987, the agent that is now believed to be responsible for the Capitola
incident struck on the opposite shore of the continent. This time, it struck higher on the
food chain. Over a hundred people became extremely ill within hours after dining on
cultured blue mussels in restaurants around Prince Edward Island in Canada. It quickly
became apparent that this was no ordinary outbreak of food poisoning. Vomiting,
cramps, diarrhea, and incapacitating headaches were followed by confusion, loss of
memory, disorientation, and (in severe cases) seizures and coma. A few exhibited
emotional volatility, with uncontrolled crying or aggressiveness. Three elderly victims
died. [Perl].
A tragic symptom of poisoning was the destruction of short term memory in about one
quarter of the survivors. They could remember nothing that happened after the
poisoning. Some were unable to recognize their surroundings or relatives. They could
learn no new facts or skills. The most severely affected lost memories several years old.
For twelve of the victims, the loss of short term memory was permanent.
Figure 1. General strategy for isolation of the toxin responsible for
amnesic shellfish poisoning. Based on a diagram by M. Quilliam and J. L.
C. Wright (Analytical Chemistry, 61, 1054 (1989)).
A band very close to the band for glutamic acid was observed in the electrophoresis of the toxic XAD-2
fraction, but not in the control fraction. It stained a distinctly different color from the glutamic acid. When
the material in the band was collected and injected onto the HPLC column, it took exactly the same
amount of time to move through the column as the toxic component found by the HPLC analysis. It also
produced exactly the same amount of toxicity as the HPLC fraction had.
Mass spectrometry was used to determine the compound's molecular weight (312 g/mol) and molecular
formula (C15H22NO6). Spectroscopic analysis revealed the presence of conjugated double bonds and
features characteristic of an amino acid. By matching the spectra with those from STN International's
Registry system, the compound was unambiguously identified as domoic acid, an triprotic amino acid:
Domoic acid in acidic solution.
Glutamic acid in acidic solution.
Glutamate (the ionized form of glutamic acid) is a neurotransmitter, so
glutamate plays a fundamental role in thought, learning and memory.
It is possible to have too much of a good thing, however. Glutamate at high
concentrations acts as an excitotoxin -a compound that kills cells by literally
exciting them to death. Excess glutamate keeps the gates that allow calcium
ions across the cell membrane open too long. Calcium ions flood into the cell,
causing it fire uncontrollably. The neuron swells and eventually bursts. The
damage cascades to nearby neurons because the damaged and ruptured
neurons release their glutamate and other excitatory amino acids,
overstimulating nearby cells. The excess calcium inside the cell stimulates
certain protein-cutting enzymes, which produce large quantities of free
radicals as a by-product. The free radicals are extremely reactive, and
damage any biochemical structure they come into contact with [Berman]. This
excitotoxic cascade is thought to play an important role in brain injury and
neurodegenerative diseases.
Domoic acid is a molecular Trojan Horse. Nerve cells mistakenly
recognize domoic acid as glutamic acid- a fatal error. Domoic acid's
structure is obviously similar to glutamic acid. But its five-sided ring
makes it less flexible than glutamate, which causes it to bind very
tightly to glutamate receptors. As a result, the excitatory effect of
domoate is 30 to 100 times more powerful than that of glutamate
[Perl].
How did the domoic acid get into the shellfish (and the anchovies eaten by
the birds at Capitola)? Remember that phytoplankton pigments were found in
the aqueous layer after solvent extraction. This wasn't quite a smoking gun,
but it was definitely a fingerprint of the killer. An extensive investigation traced
the domic acid to an obscure species of needle-like diatom*, called Pseudonitzschia pungens (shown in the title banner at the top of this page). Pseudonitzschia has been found in oceans around the world, so further outbreaks
are possible in many locations. Commercial shellfish and seafood is now
monitored regularly for domoic acid, using HPLC to identify the toxin. The
screening and testing procedures have so far been successful- not a single
instance of domoic acid poisoning in humans has been reported since the
1987 outbreak.